Earth's Magnetic Field

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The earth's magnet is thought to be formed by circulating electrical currents in the outer core, which would then decay just as any other magnet would. The half-life of decay of the earth’s magnetic field is 1,400 years. The chart below shows the strength of the earth's magnet over time1:

Date Strength Yearly Decay
1835 8.558 0.0070 (.082%)
1845 8.488 0.0036 (.042%)
1880 8.363 0.0032 (.038%)
1885 8.347 0.0028 (.034%)
1905 8.291 0.0066 (.080%)
1915 8.225 0.0076 (.092%)
1925 8.149 0.0061 (.075%)
1935 8.088 0.0023 (.028%)
1945 8.065 0.0030 (.037%)
1955 8.035 0.0022 (.027%)
1965 8.013
===== ===== Rate predicts…2
2000 7.872
3000 4.823
4000 2.954
5000 1.810
6000 1.109
7000 0.679
8000 0.416
9000 0.254
10000 0.156

This half-life would mean that 100,000 years ago, the earth’s magnetic field would have been comparable to a neutron star, and would not have been able to support life. This is strong support that the earth is young, rather than billions of years old as the old-earth model requires.

Scientific instruments are not the only mechanisms that have ever existed for measuring the Earth's magnetic field. Ovens used by ancient civilizations and the igneous rocks making up the ocean floor are two of the more obvious examples. Both record the direction and strength of the magnetic field as it was at the time they were last heated, and both prove conclusively that the hypothetical exponential decay of Earth's magnetic field has not occurred (according to the young-earth theories, the magnetic field was many times greater only a few thousand years ago, a hypothesis that is clearly at odds with the above-mentioned evidence).

Instead, the evidence shows that the magnetic field has fluctuated back and forth in strength as well as direction. These fluctuations are clearly observed in places where the stratigraphy (i.e. which rocks are older than which rocks) is obvious due to either layering or distance from a sea-floor spreading ridge. The decrease measured in the past few hundred years, therefore, is nothing more than a downward trend as part of an overall fluctuation, and has no implication for the age of the Earth (for a more detailed discussion of this issue, see Thompson (1997),

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